Studies are in progress in the following areas, in elaboration of previous work from this laboratory: 1. Subunit structure of myosin: Characterization of subunit composition and interaction of myosin by ultracentrifugal, electrophoretic, and other physical chemical methods. 2. Studies of structural and enzymatic changes in myosin as related to cardiac hypertrophy in canine tissue. 3. Role of subunits in myosin ATPase. Recombination and hybridization experiments on relation of specific ATPase to subunit composition. 4. Effects of pressure and temperature on enzymatic properties of myosin, actomyosin, and Ca-regulated system, with special reference to adaptative phenomena.